This invention relates generally to power supply systems, and more specifically, to electronic controlled regulation of the power supply systems.
Power systems are commonly used to convert alternating current (AC) voltage provided by a power company to a desired voltage for various loads, such as AC and direct current (DC) motors. Many countries use AC voltages having differing magnitudes and frequency. A full wave bridge rectifier is often used to convert an alternating current voltage to a direct current voltage. A disadvantage with known bridge rectifiers is that they produce a current waveform that contains multiple short current pulses or spikes synchronized to the power supplier""s voltage signal. As the proliferation of small appliances and other electronics has occurred, power suppliers have experienced a detrimental effect on their distribution systems caused by the widespread current pulses being injected onto the distribution system. The problem is severe enough that government regulations are becoming common to establish regulations that would minimize the problem. The spikes generate harmonic signals into the distribution system often known as electromagnetic interference (EMI).
Another common problem for power suppliers is known as the power factor issue. Optimally, a load in a power system would be purely resistive. A purely resistive load will result in maximum power efficiency and thus a power factor of one. The power factor is defined as the cosine of the phase angle between the voltage applied to a load and the current passing through it. For example, a purely resistive load has a power factor of one where the voltage and current are always in phase. A power factor of one is optimal for power delivery and this condition is shown in FIG. 1. However in reality, loads typically possess a significant amount of impedance (both inductive and capacitive components) that significantly lowers the power factor causing the voltage and current to be out of phase. An example is shown in FIG. 2.
Prior solutions to address the EMI problem have included correction circuitry known as power factor correctors. Power factor correctors improve power distribution efficiency and reduce AC line EMI. Power correction circuitry is often used in industrial control and is increasingly required in home appliance dues to increasing governmental regulations. Such power correction circuits are typically isolated and independent integrated circuits that are separated from conventional voltage regulation control circuitry. Such integrated circuits typically have no compensation for the commonly known problem of component value variation caused by temperature variation. Also, such circuits often require precision external components that add significant cost in order to increase efficiency. Additionally, advanced digital signal processors (DSPs) having high data throughput are often used to control advanced voltage regulators. Less expensive power correction circuits typically must be factory adjusted to compensate for manufacturing variations of the components. Another approach in improving power correction circuit performance is to use a less expensive processor such as an eight-bit microcontroller in conjunction with very high precision components, such as a precision comparator. If a lower precision comparator is used in such an application, offset and gain errors commonly associated with analog comparators contribute significantly to reduce the efficiency of the system.